Simplify the following expression: $y = \dfrac{9}{10n} + \dfrac{8}{7n}$
Explanation: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $10n$ and $7n$ $\lcm(10n, 7n) = 70n$ $ y = \dfrac{7}{7} \cdot \dfrac{9}{10n} + \dfrac{10}{10} \cdot \dfrac{8}{7n} $ $y = \dfrac{63}{70n} + \dfrac{80}{70n}$ $y = \dfrac{63 +80}{70n}$ $y = \dfrac{143}{70n}$